During adjusting a shafting center of vertical hydroelectric generating set, a rotor needs to be driven by an external force so as to check the radial swinging angle of each section. Thus, an even and smooth driving rotation speed, and accurate stop points are required. Furthermore, the rotor should be in a thoroughly free status at each stop point without any disturbance external force exerting on the rotor. Moreover, it should be convenient and quick to operate in the field. However, the driving method provided by most manufacturers still employs manual driving and came hauling, which causes low safety, high labor intensity and inefficient works. The applicant of the present invention has two Chinese patents on improvement of the conventional barring method by providing a new automatic rotor turning gear: one is Chinese Patent No. 92219180.8 and the other is Chinese Patent No. 99222132.3. However, the two patents still have some shortcomings as follows. The automatic rotor turning gears have a low concentricity with the rotating devices. There is a rigid connection between the automatic rotor turning gear and a frame of the rotating device, so that a little deviation between axes of the rotor turning gear and the rotor may causes an excessive and unstable driving moment of force, which requires a long time to adjust. Arms of force of the above devices is very long and the pinion gear is assembled in a suspension arm structure, so the two structures may be easily deformed under stress to cause incorrect engagement between gears. Moreover, wires may be twisted because the motor is turned along with the device.